We could do a lot to better serve the SU community if we killed off some tags en masse. If we're going to maintain many confusingly similar sites, perhaps we should just reject tags like nginx which really don't belong here. An info bubble or a redirect to ServerFault seems to be at hand. I can think of a lot of tags like this too.
Many of these questions are easy and moreover, there is very little activity or interest in them. Defining the scope the Q/A site is prime to it being useful, permitting people to make accidents that technology could easily resolve is kind of silly.
I think a mechanism that does this could even be extended to the title. If the title has
nginx perhaps the user should be immediately prompted with a suggestion that the question is probably not best asked here.