My horse is an American bashkir curly. His mane is split so half of his mane is on one side, half on the other. In the middle along his crest he's got all this gross stuff like dandruff and scurf and I think dried crusty gushy shampoo from the last time I washed him!!! It's gross and when I scrub it with my finger it doesn't come out. Should I wash it or how can I get it out???