The flood story is covered in many cultures.
These generally co-occur in water rich areas, such as low-lying coastal regions or flat, regularly inundated river plains. Thus, flooding in relatively populated early centers of civilization is likely to be a common experience across human cultures, purely by the geographical reality of proximity to water.
Furthermore, recording such events is natural in a literate civilization since the destruction a nontrivial event might cause against food, shelter and population would affect all echelons of society.
Being in many cultures isn't evidence against the story, as it seems you are trying to imply.
It could simply mean there was one huge flood and lots of cultures recorded it.
I am aware there is no scientific mechanism to cause a worldwide flood, this is explicitly about divine intervention. (i.e. a miracle, not creationism pseudo science).
However, since there are reasons other than reason and evidence for people to believe in a flood, no amount of reasoning or evidence will change those beliefs, so I propose we focus on the tantalizing science fiction implications instead.
1. Why only those? Isn't it global?
2. This comment has no value without an academic paper to reference. If nobody has studied it, this is just hot air. If someone has, you are expected to link to it in these lands.
3. It's "Africa". Not "affrica".
It worked for you, didn't it? It also worked for me. That's two of us. There are more. Keep the uh... "faith".
Also note that floods don't simply go in a straight line from A->B. In practice because towns are built on the more stable land, what you'd see happen is pretty much the worst possible scenario : the water would surround cities, first making most roads unusable (non hardened ones because they become mud, hardened ones because some parts of them collapse). Then the water level would rise until nothing remains above the water level. (I've got some experience living in Northwest Europe, and every 20 years or so you get introduced to this problem firsthand)
Of course, even though the affected area was huge, it was still a local phenomenon.
[1] http://en.wikipedia.org/wiki/Black_Sea_deluge_hypothesis
That said, if there never was such a flood there would likely be evidence that it never happened.
What would evidence that there was never a global flood look like? One example might be "lack of a global species disruption in the fossil layer". But that's just absence of evidence again.
I think there are some predictions you could make there. However every single one of them is just so far divorced from what we observe that they aren't even worth enumerating.
"Proof" is a complicated word. People typically take it to mean "slam-dunk, 100%, without-a-doubt proves the case." But little in science ever works like that. Math, sure, where you can prove things analytically. But when trying to "prove" things about the universe, you have to collect bodies of evidence, and see how well that evidence matches expectations.
So, when you go out looking for something, and despite your best efforts, cannot find it, then that may not "prove" that something did not happen, but it is good evidence in support that it did not.
Despite centuries of scientists looking hard for evidence of it (and knowing what kind of evidence they are looking for, adn being able to get it), they've been unable to get any. That's as strong evidence of the inexistence of a phenomenun as you can get.
Given Christianity has roots in Judaism and Judaism probably has some roots in Sumerian religion, I'm not sure if you could say that. Religions evolve from other religions, and in a geographic area, are likely to have common ancestors.