Without any presence in foreign countries, the most the foreign country can do is block the offending website or infrastructure provider. I guess they could also request extradition, but most countries only extradite citizens if what they did was also illegal in the home country.
Enforcement is, of course, a separate matter. The country may not be able to reach you without some sort of agreement with your home country; but if you ever visit a country with which it does have an agreement, you could find yourself taken away to answer to the law.
Well, yes, kinda. But the Saudis will not be successful in extraditing you, most likely. However they can still block your services, and Allah help you if you decide to travel there after you've been found guilty of violating their laws.
Then again, not as bad as the US is on and about... Just ask Mr Dotcom...
Assange and Wikileaks is similar - Assange is an Australian citizen in the UK, but is being extradited to the US for breaking US law via a website. He is not being charged with any offences (to do with this) in either the UK or Australia.
If your website blasphemes and can be reached from Saudi, then the relevant authorities there could push for you to be extradited to face charges in Saudi (if your country and Saudi have an extradition treaty). It doesn't happen, but that doesn't mean it couldn't happen.