I've been moisturising my feet with coconut oil and that seems to be cleaning the dirt out of the cracks in my heels too. And I am wearing socks around the house during the day (partly so I don't get oily footprints on the carpet and floorboards and partly to help the oil soak in).

The problem with cracked heels is that you have to keep on top of them. Once fixed, they don't tend to stay fixed unless you keep maintaining them.