[SOLVED] problem with rsync exclude

I use rsync to backup my thunderbird mail directory every night. I am tring to exclude the cache2 directory using the following command:
rsync -avzrcp --exclude '/home/xxx/.thunderbird/yc4iwpsm.default-default/cache2' /home/xxx/.thunderbird /media/nas2/xxx

In the the test, the cache2 directory (and its contents) were copied. I have obviously made a mistake but so far don't see it.

Thank you.