This hook is called after a call to update_metadata succeeds.
<?php add_action( "updated_{$meta_type}_meta", $function_name', 10, 4 ); ?>
where $function_name is the name of the function to be called and $meta_type is the type of metadata that was updated.
Note that unlike updated_postmeta, the $_meta_value param is not serialized.
For example, to respond to updates to user metadata:
<?php add_action( 'updated_user_meta', 'my_update_user_meta', 10, 4 ); function my_update_user_meta($meta_id, $object_id, $meta_key, $_meta_value) { //do stuff } ?>
updated_(meta_type)_meta is located in wp-includes/meta.php
.