Q: Assuming one makes the janabāh ghusl, as required, and realizes, post-completion, that there had been a skin obstruction on his/her body (e.g. a dried semen stain) which had prevented water from coming into contact with that particular area, what ought one to do?
A: The aforementioned ghusl is void. One must initially remove the obstruction and then purify the previously-obstructed area. Then, one must rinse that area whilst having the intention to complete one’s previously defective ghusl. Assuming the obstructed area was located on the right hand side of the body, one must then, according to obligatory caution, rewash the whole of the left hand side (as part of one’s intention to make the ghusl).