Forum:Mirrorforce/wall of thorns, negated attack?

Hey, I recently got both Mirror force and Wall of thorns. And I notice they don't explicitly say that the attack that's declared is negated. I just wanted to be sure I'm clear on this. Is the spell speed faster then the attack and destroys the creature thus negating the attack since the creature is gone? Or does the attack go through, then all the creatures get destroyed?