After logging off, user is able to see the workbench page by pressing back button of the browser
Used this in custom module and it works

&lt;?php 
/**
 *Implements hook_init().
 */
function MY_MODULE_init() {
  drupal_add_http_header('Cache-Control', 'no-cache, no-store, max-age=0, must-revalidate, post-check=0, pre-check=0');
}