Rules · PlanesAdvisor

801.7 A triggered ability doesn’t trigger unless its trigger event happens entirely within the range of influence of its source’s controller. Example: In a game in which all players have range of influence 1, Alex is seated to the left of Rob. Rob controls two Auras attached to Alex’s Runeclaw Bear: One with the trigger condition “Whenever enchanted creature becomes blocked,” and one with the trigger condition “Whenever enchanted creature becomes blocked by a creature.” Alex’s Runeclaw Bear attacks the player to Alex’s left and becomes blocked. The ability of Rob’s first Aura triggers because the entire event (Runeclaw Bear becomes blocked) happens within Rob’s range of influence. The ability of Rob’s second Aura doesn’t trigger, however, because that event includes the blocking creature, which is out of Rob’s range.

801.7a If a trigger event includes an object moving out of or into a player’s range of influence, use the game state before or after the event as appropriate to determine whether the triggered ability will trigger. See rules 603.6 and 603.10. Example: Carissa and Alex are outside each other’s range of influence. Carissa controls a Runeclaw Bear owned by Alex and they each control an Extractor Demon, a creature which reads, in part, “Whenever another creature leaves the battlefield, you may have target player mill two cards.” The Runeclaw Bear is destroyed and is put into Alex’s graveyard. The ability of Alex’s Extractor Demon doesn’t trigger because the leaves-the-battlefield event was outside Alex’s range of influence. The ability of Carissa’s Extractor Demon does trigger, even though the creature is going to a graveyard outside her range, because the leaves-the-battlefield event was within her range. (refs: 603.6)