There is no server event that gets triggered when a user uses the clear function. The logical event would be to trigger the SelectedIndexChanged since it is essentially going from a value to nothing, therefore changing the selected index. I'm sure that since the world is slowly trying to forget about server programming and concentrating on Java that there is some java solution that won't do me a hill of bean worth of good.
My point, would it be so bad to have the clear function trigger something?