I am here to tell ya How to clean your cookie sheets with the stuff I call Kitchen "Miracle" Cleaner! You put about 1/4 cup of baking soda in a small glass bowl and squirt in hydrogen peroxide until it makes a nice paste. Then you rub it on the offending dirt/stain/grease...whatever! You can usually just use an old dish cloth...but you can also use a small sponge as well.
I was amazed at how well this stuff worked! I feel like I got brand new cookie sheets...seriously I have tried cleaning these darn pans with everything under the sink but was never able to get that sticky icky burned on gook to come off.