601.14b.

If a spell or ability creates an effect that prevents damage that would be dealt by a source, it can affect only sources within the spell or ability's controller's range of influence. If a spell or ability creates an effect that prevents damage that would be dealt to a creature or player, it can affect only creatures and players within the spell or ability's controller's range of influence. If a spell or ability creates an effect that prevents damage, but neither the source nor the would-be recipient of the damage is specified, it prevents damage only if both the source and recipient of that damage are within the spell or ability's controller's range of influence.

Example: Rob is within Alex's range of influence, but Carissa is not. Alex controls an enchantment that says, "Prevent all damage that would be dealt by creatures." Carissa attacks Rob with a creature. The creature deals combat damage to Rob.

Example: Rob is within Alex's range of influence, but Carissa is not. Carissa plays Lightning Blast ("Lightning Blast deals 4 damage to target creature or player") targeting Rob. In response, Alex plays Honorable Passage ("The next time a source of your choice would deal damage to target creature or player this turn, prevent that damage. If damage from a red source is prevented this way, Honorable Passage deals damage equal to the damage prevented this way to the source's controller.") targeting Rob. The damage to Rob is prevented, but Honorable Passage can't deal damage to Carissa.

Example: Rob is within Alex's range of influence, but Carissa is not. Carissa attacks Rob with a creature, and Rob blocks with a creature. Alex plays Holy Day ("Prevent all combat damage that would be dealt this turn.") Carissa and Rob's creatures deal combat damage to each other.