How are nexus feats treated?

[ProfectusInfinity]

By "nexus," I'm talking about dimensions in fictional verses that are depicted as places where multiple realities converge; probably half of all 2-A and above verses have a "nexus of all timelines" realm or something similar in their cosmology. My question is, how exactly should feats affecting these kinds of places be treated? Shouldn't they be considered chain reactions? A popular example of a nexus like this is Yggdrasil from Marvel Comics. It's one thing if someone standing around in the base multiverse were to affect the World Tree just from shockwaves of their power, now that's a clear-cut feat. But if someone is stated to specifically need to go to the World Tree to destroy the multiverse, how isn't that a chain reaction feat or otherwise situational?