The problem with the above suggestion is that it will also delete the track listing within iTunes itself, along with all the metadata (playlists, playcount, last played date, etc.)
A better way to go about this, I've found, is this:
Turn off iTunes Match. Quit iTunes.
Hold down the OPTION key while re-launching iTunes. A dialog will appear. Create a brand new library, call it whatever you want ("iTunes TEMP" should do.) Then turn on iTunes Match. It will then download the whole index of songs that have been sent to the cloud (via matching, uploading, or because you've purchased them) in this new library you've created. Then you can simply select all of these tracks, hit delete -- and it will delete these songs from iTunes Match. Your iTunes Match is now empty. Then turn off iTunes Match , and quit iTunes.
Hold down the OPTION key while launching iTunes... and this time, select your original iTunes library.
After you've determined that all is well, you can safely delete that other "iTunes TEMP" folder.