Drupal (6) login & logout issue

Drupal (6) login & logout issue

/**
 * Implements hook_init().
 */
function mymodule_init() {
  // Override Drupal default header.
  // See http://www.journeymm.com/blogs/drupal/drupal-loginlogout-caching-problem
  // and http://sriramk.com/blog/2007/06/firefox-and-ie-deal-with-no-cache.html
  header("Cache-Control: no-store, no-cache, must-revalidate");
  header("Cache-Control: post-check=0, pre-check=0", FALSE);
}