you can use lemon or lemon juice to rub your hands...
crabtree & evelyn also has a "critus" handwash which can remove the odor of onion and garlic
btw, 吉之倒十蚊店出售一件專門用來去除洋蔥或蒜頭味的蛋型金屬 (i don't know the exact name of this product... sorry), you can use it to rub your hands when washing.