Considering that the movies have made no mention of the power of Saruman's Voice, I'm not at all surprised that the Scouring would be left out. Remember that Saruman was stripped of all his sources of power with the exception of his Voice. It's the Voice that allowed him to escape imprisonment in Isengard and allowed him to take over the Shire. Without this key ingredient Saruman's takeover of the Shire and the subsequent Scouring don't make much sense.

Bruce