Is there a way to automatically remove all the invalid entries from an iTunes music library?

"There's quite a few great AppleScripts available at dougscripts.com. To remove invalid entries, you can use Super Remove Dead Tracks v2.1.

What it does:

Surveys iTunes for tracks whose files
are no longer available (as indicated
by a ""!"" next to their names) and
removes them. Any playlists that
subsequently contain no tracks will
then be deleted. Progress is displayed
every 500 tracks.

To scan for new tracks, you can use iTunes Library Sync (an Automator script):


Place the script in /Username/Library/Workflows/Applications/Finder
(where Username is your username)
If the workflow directories don't exist, you have to create them
manually.
When done, the script will be available to you with a simple right
mouseclick (on some free desktop
space).
Select Automator -> Synchronize Library and your done.


Note: When running this script for the first time, open Automator and
disable the “Date Modified” rule
because we want to add all the songs
first. When done you can enable the
rule again.

Both tools are freely available.

Source"