One thing about Chaos Gods and Tyranids that I don't understand

I just have a question about the area of influence the Chaos Gods have in the universe - as the Tyranids ale closing in from all sides of unknown space towards Empires system, devouring everything in their path, is it possible that they've also destroyed systems/galaxies that were under the influence of Chaos Gods? Or is it known to us if there weren't any races/species affected by them outside the known space?

Just to add, I'm a big fan of Warhammer but I'm not exactly expert on the lore. Would love for somebody to give me more details. Thanks!