Washing a musalla that was touched by a shoe

My mother uses a sandle which she takes to the toilet also. A few times she accidentally stepped on my musallah. I touched the part and it was not wet. With my hand only, I clean the dust without using any water as I am not sure where she exactly stepped on. She also stepped on the musallah with her shoe which she wears when she goes outside. Do I have to wash the musallah? I am currently reading salaah on the same musallah. I have doubts about another musallahs because my nephew urinated on them and the house worker washed them. I dont know if she washed it thrice or not. Can I read salaah on them as she used a detergent?