Honestly, I would have a vet out. That looks really painful. You know, no hoof no horse and all that. No heel no horse either. Cleaning it might seem like the right thing to do but if it is something that likes moisture??? Or you could do more damage with any harsh cleaners or disinfecting. At least call the vet and talk to them. Perhaps you should keep the foot wrapped? Or not wrapped? I personally wouldn't wrap because of the location. But you don't know until you have a vet see it. It could be greasy heel as well as something else.