- You may be looking for the concept of one's "prime universe".
The planet Iytea, known to its inhabitants as the Prime World and also referred to as the Iytean homeworld, was the home planet of the Iyteans and as such, the central node of the interstellar Iytean Confederacy. It was located in the Mutters Spiral, with Earth's system being located on the outer fringes of the Confederacy.
Around 3000 BC, the planet was caught in the crossfire of the Anar-Isari wars and was "devastated", along with most of the colony planets making up the Confederacy, leading to the near-extinction of the Iyteans. (GAME: The Iytean Menace [+]J. Andrew Keith, The Doctor Who Role Playing Game (FASA, 1985).