The control of all monsters on the field returns to the owners.
Rulings
Individual Card FAQs
When "Remove Brainwashing" is activated, monsters like "Lava Golem" & "Parasite Paracide" will return to their owner's side of the field, monsters revived with "Monster Reborn" return to their owner's side of the field, monsters taken with "Exchange" and played normally return to their owner's side of the field, etc.
When "Remove Brainwashing" is already active on the field and a switching effect is activated, or "Remove Brainwashing" is chained to a switching effect and is thus active before the switching effect resolves, control switches due to the effect but then switches back to the original owner because of "Remove Brainwashing". So for "Creature Swap", control is changed but then control goes back to the original owners. This means that if you give control of "Griggle" or "Ameba" to your opponent, their effect IS activated even though "Griggle"/"Ameba" then returns to the original owner's control afterwards.
If "Monster Reborn" is activated and "Remove Brainwashing" is chained (or was already active on the field), the monster goes to the side of the field of the player who activated "Monster Reborn", then switches back to the original owner immediately afterwards.
If "Remove Brainwashing" is activated and a player already has 5 monsters on the field, the returning monsters are destroyed. If multiple monsters are returning to the owner due to "Remove Brainwashing", and he does not have enough room for all of them, the player who controlled the monsters chooses the ones that are destroyed and the ones that return successfully.
When "Snatch Steal" is active, the +1000 Life Points effect is applied even if "Remove Brainwashing" has returned control of the monster to the original owner.
"Remove Brainwashing" has no effect on a Monster Card equipped to "Relinquished" or "Thousand-Eyes Restrict", and the Monster Card remains where it is, because it is an Equip Spell Card.
If "Remove Brainwashing" is destroyed, control does not revert again, so if I activate "Change of Heart" and my opponent chains "Remove Brainwashing", control of the monster comes to me and then reverts to my opponent. Then, later in the turn, if "Remove Brainwashing" is destroyed with "Heavy Storm", control does not revert back to me and remains with the original owner. (The same for "Creature Swap", etc.)
If your opponent takes control of your monster with "Snatch Steal", etc., and you activate "Relinquished"'s effect on your next turn to equip the monster to "Relinquished", and your opponent chains "Remove Brainwashing" to "Relinquished"'s effect, control of the monster returns to you before "Relinquished"'s effect resolves and, since you cannot use "Relinquished"'s effect on monsters on your side of the field, "Relinquished"'s effect disappears.
Control of "Blindly Loyal Goblin" cannot change even because of "Remove Brainwashing", so if "Blindly Loyal Goblin" is Summoned due to "Monster Reborn" or using "Exchange", the original owner will not control "Blindly Loyal Goblin".
Netrep Q&As
Q: Player 1 has all 5 Monster Zones filled and Player 2 activates “Monster Reborn” on a Monster in Player 1s Graveyard. What happens to the selected Monster if “Remove Brainwashing” is either already active or activated after “Monster Reborn” is resolved? Since the Monster can't fit back on its owners Field would it be destroyed, would nothing happen until there is an open slot or something completely different? A: The monster would be destroyed. Curtis Schultz, 12/04/2003
Trap|
Continuous