Leyline grants hexproof only to the player controlling leyline, not to his/her creatures or other permanents.
Hexproof means that the object having it cannot be targeted by spells or effects of opponents.
Scourge's trigger is not optional so you have to choose a legal target for its effect if possible. If your opponent has only Leyline in play, your choices are limited to creatures and yourself.
January 12, 2017 8:19 a.m. Edited.
Boza , thank you very much. The leyline example was only to ilustrate one example, and yes, it would grant hexproof only to him.
January 12, 2017 8:23 a.m.
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