A command line script, shell/brim-fpc.php, is shipped with all recent versions of our Full Page Cache. The script can remove by tag, expired pages, or everything. Running the script without options will display the usage help.
However to remove a CMS page from the cache you just need to know the page's id and run the following command where "1" is the pages id:
php -f brim-fpc.php --clean --tags BRIM_FPC_CMS_PAGE_1