Must the entire garment be washed upon waking if there are traces of madhi, but the affected part is not identified?

It is not obligatory to wash the entire garment; rather, only the part that is certainly known to have been affected by madhy (pre-seminal fluid) should be washed. It should not be washed merely out of doubt or waswasah (whispers/obsessive thoughts), because the original state of the garment is purity, and its impurity is not established except with certainty.