This is how I clean my own cast iron skillets, cast iron lids, and cast iron Dutch ovens. If you are unsure about my method, don't try it. It works for me, because although my cast iron is very old, it has no breaks or cracks. I have had really nice results this way! For self-cleaning ovens!
*** I read a review (and thanks for it really!) that this will delete the non-stick qualities. I should have made my intention clearer, since this is what I do when cast iron has too much old, old build-up or looks too disgusting from non-use. I am happy someone said something though! I use my cast iron alot, so mine continues to stay nice because of that.