Nix

Nix is one of the worlds located beyond the Nine Realms still watched by Heimdall.

History
When the Bifrost Bridge was destroyed many of the Nine Realms and the worlds beyond were engulfed into chaos, when organizations such as the Marauders or the Badoon seized to opportunity to loot these worlds without asgardian interference.

It is presumed that when Thor and the Asgardian Army pacified the realms, Nix was one of the worlds visited to drive the invaders away.