It's covered in 6E1 133. I don't see a reference in CC, which is what I seem to remember you have. Short version--build a power to block or overcome the highest level effect you will allow in your campaign (if no one can have more than 10DCs normal damage, 60 DEF blocks that). Then you declare that to be an absolute effect.
Anything using an Absolute Effect has to be evaluated against your own campaign limits if you want to price it correctly for your game.