node_load uses db_query, which uses mysql_query -- so there's no way to easily change the database's cache through that function.
But, node_load does use Drupal's static $nodes cache -- It's possible that this is your problem instead of the database's cache. You can have node_load clear that cache by calling node_load with $reset = TRUE (node_load($nid, NULL, TRUE).
Full documentation is on the node_load manual page at http://api.drupal.org/api/drupal/modules--node--node.module/function/node_load/6