Let $R$ be a Noetherian normal domain and $I$ a nonzero $R$-ideal. Show that if $I$ is divisorial, then every associated prime of $I$ has height one. ($I$ is said to be divisorial if $(R:(R:I))=I$, where $(R:I)=\{k\in K\mid kI\subset R, K$ is the field of fractions of $R\}$.)
It seems like I have to prove that by localizing $R$ at every associated prime $P$ of $I$, $P_P$ is invertible.