Drupal - How to clear cache externally?

If you are running a script, you'll likely benefit from using Drush. With the Drush php-eval and php-script commands, you can easily call a snippet of php code (such as the examples shown in other answers to this question) after bootstrapping Drupal. Without Drush, you would have to set up a web service and use wget or curl to run your code, or try to call the Drupal bootstrap code yourself. Better yet, Drush even comes with a built-in command to clear the cache, so you don't need to worry about writing any php code at all, if that's all you want to do from your script. Just use:

cd /path/to/drupal/sites/default && drush cache-clear all

You may also wish to learn about site aliases; if you define an alias called @site, then you can instead use:

drush @site cache-clear all

If you just want to clear one or two particular cache bins you can use cache_clear_all() (assuming your script has Drupal bootstrapped):

cache_clear_all(NULL, 'cache_views');
cache_clear_all(NULL, 'cache_views_data');

I suggest register menu and externally call it ,in call back of it put your code(clear cache )

function yourmodule_menu() {
    $items = array();
    $items['customclearcache'] = array(
        'title' => 'clear cache',
        'description' => 'clear cache',
        'page callback' => 'yourmodule_clear_cache',
        'access callback' => TRUE , // or any access you need
    );
    return $items;
}


 function yourmodule_clear_cache(){
   cache_clear_all(NULL, 'cache_views');
   cache_clear_all(NULL, 'cache_views_data');
   drupal_set_message(t('cache clearing completed'));
   drupal_goto("node"); // or any page you want
}

and you can clear cache with calling this url : yoursite.com/customclearcache.

Also if you installed drush clear cache with it drush cc all

   //first go to your installed site path
  $cd /path/to/drupal 
   $drush cc all