I say, and with God's success: If the semen is wet, it can only be purified by washing; as reported by Al-Daraqutni in his Sunan from Aisha, may God be pleased with her, who said: "I used to rub the semen off the garment of the Messenger of God, peace be upon him, when it was dry, and wash it when it was wet." See: Tanweer Al-Absar 1: 207-208, and Fatawa Qadi Khan 1: 25, and God knows best.