The Cleansing is an event that occurs during Lexx 1.4 "Giga Shadow" in which the entire population of the League of 20,000 Planets (and possibly animal life as well) are transported to the Cluster where they are stripped of their flesh and protein by Security Drones using a surreal clown-faced machine. Unlike the Protein Bank, which only harvested organs from criminals or reprimanded workers, the Cleansing by contrast appears to have indiscriminately eradicated almost all intelligent life in the entire league of 20,000 planets.
Over the course of the cleansing the protein reclamation is used to feed the Giga Shadow, a gigantic survivor of the Great Insect War, so that it will be able to emerge from beneath the Cluster and dominate the universe as a result of the ensuing Rebirth.
It is unknown how many survived the Cleansing, though some worlds such as Ruuma and Woz appeared to have been forgotten by the Divine Order, or were not deemed worth the investment of resources to ferry their meagre populations to the Cluster. Meanwhile other worlds outside the League of 20,000 Planets, beyond the Frontier, have survived unharmed thanks to their being beyond the reach of the Divine Order, though the Rebirth would have likely resulted in their demise eventually if it hadn't been stopped.