I bought a pre-seasoned cast iron grill pan (my first cast iron) and I'm having trouble cleaning it. I use hot water and a scrub brush but there always seems to be a layer of grease that doesn't come up. I know grease or oil is what seasons the pan but I feel like the pan's dirty because it's brown grease. After I've washed the pan should anything come off on my finger when I rub it? I'm sure I could get this grease off if I scrub enough but I don't want to scrub the seasoning off. Thanks in advance!