This is a very simple and elegant exploit i discovered the otherday.
If this is a repost, i failed to find anything while searching for:
Spellreflect
Mage exploit
Cast through immune
Scorch
Here is what you do, when you see a mob cast a spell that reflects spells, just start spamming scorch. It goes through the shield at a rate of about 95%.
I'm not sure this works on warriors, as i ahvent got the opportunity to test it..