What is the fictional universe that XXX appears in?
Negative Zone
In the Blink mini-series, it is established that there is in fact only one Negative Zone in the multiverse of Marvel Universe, with exit points to different realities and timelines, as the Blink from the Age of Apocalypse found herself in a Negative Zone that still remembered the Fantastic Four's role in defeating Annihilus despite the fact that the team never existed in her world.
Marvel Universe