What is the ruling on the scab formed over wounds; is it pure or not, knowing that it does not come off with washing and no color or taste transfers from it?

The scabs formed on wounds and attached to the body are pure, and there is no obligation to remove them. Rather, their ruling is the same as the skin they cover. There is no obligation to remove them, nor to repeat ablution after removing them. One must abandon obsessive thoughts and not succumb to them.