A good scouring pad (no steel wool or detergant, of course, but those green wiry ones made of stiff plastic fiber) and some baking powder paste. You can rinse that off when you are done, but even if you leave residue, it won't be a big deal, because it is just sodium bicarb (some people use it for buffering, but it has cleaning properties as well, many people use it on the inside of fridges).