Tome scour says target player on it, so it only targets one player. The caster would target a player, and that player would mill the top 5. Note that the player can be anyone, including his teammate or himself.
Cards that affect both heads in a 2hg game would say things like each opponent, like Blood Tithe, or each other player, like Urborg Syphon Mage
Thanks
:EDH:
WR Gisela, Blade of Goldnight (HOLD/100) WR
WB Teysa, Orzhov Scion (HOLD/100) WB
Cards that affect both heads in a 2hg game would say things like each opponent, like Blood Tithe, or each other player, like Urborg Syphon Mage
The latest Comprehensive Rules are also good, and can be found here.