Can I clear front page cache only?
Drupal 6 and 7 use the URL of the page as the cache ID (the $cid, see drupal_page_set_cache()).  This should work.

$url = url('&lt;front&gt;',  array('absolute' =&gt; TRUE));
cache_clear_all($url, 'cache_page');


You will need to adjust the logic a bit if you can access the site through multiple URLs.