Well Looks like they CAN be saved-- usually I throw mine away!!

HERE IT IS!
How to clean your cookie sheets

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 your fingers...but you can also use a small sponge as well.