Is semen considered impure if it is discharged onto the glans after the pre-seminal fluid has dried, without performing ritual washing (istinja') or wiping (istijmar)?

Semen is pure, while prostatic fluid (madhy) is impure. Semen becomes impure if it mixes with prostatic fluid while both are wet, or if one of them is wet. Impurity is not transferred by mere doubt, because the original state is purity.