Meg's Chrome Wheel Cleaner will blow that brake dust right off. But, its corrosive so you would have to be super careful with it, and I would only let it dwell a few seconds... I would use clay first though, thats safer and should do it, just may take more time.
Recently, I tried several products
To clean my rotor hats and nothing worked at getting the brake dust off except the Meg's. Check out the pics:
Before Meg's Chrome Wheel Cleaner: