WordPress at a glance
action is not described

trashed_post_comments action-hook . WP 2.9.0

Fires after comments are sent to the trash.

Usage

add_action( 'trashed_post_comments', 'action_function_name_2921', 10, 2 );
function action_function_name_2921( $post_id, $statuses ){
	// action...
}
$post_id(int)
Post ID.
$statuses(array)
Array of comment statuses.

Where the hook is called

wp_trash_post_comments()
wp-includes/post.php 2954
do_action( 'trashed_post_comments', $post_id, $statuses );

Where the hook is used (in WP core)

Does not used.