We can create a page which will clear the cache when it is loaded, and then add a new menu item linking to that page.
1. Create a new page with the following PHP code.
<?php drupal_flush_all_caches(); drupal_set_message('cache flushed.'); ?>
2. Make sure the body is set with PHP code input text format.
3. Add a new menu item.
So now whenever the user click the new menu item link, the Drupal cache will be cleared. And this approach also works in Drupal 7.
Reference: A page to clear your cache