I agree with the premise, but it depends on your workplace. I struggle with colleagues who don't even both checking if the spot is available.
No, the best that I can do that fits in the work culture is to block out a few “GTD” (actually I call them “GSD/Get Shit Done”)hours at strategic times during the week.
I want to point out that I do attempt Inbox Zero because it’s a method for dealing with a problem that’s within my control but also within “normal” working parameters.
I had the same issue in my last job at a large enterprise. What I found out was that many people actually didn't know how to use that feature.
If so, I do not bother to decline such a meeting, I just do not show up.