If the target spell is an illegal target when Psychic Strike tries to resolve, Psychic Strike will be countered and none of its effects will happen. The target's controller won't put any cards from the top of his or her library into his or her graveyard.

You may target a spell that can't be countered. When Psychic Strike resolves, the target spell will be unaffected, but its controller will still put the top two cards of his or her library into his or her graveyard.