The Cleansing of the Nine Houses represents one of the battles fought during the Old Sith Wars, and it unfolded not long after the defeat of Exar Kun during the Great Sith War.
While the specifics have faded into obscurity, evidence suggests it was a localized civil war within the Tapani sector. The Jedi Order, in conjunction with House Pelagia, engaged in combat against the Sith-corrupted Mecrosa Order of assassins, who received backing from House Mecetti. As the conflict raged, House Melissus and House Barong were taken over and incorporated into House Mecetti.