WordPress at a glance
function is not described

wp_cache_set_comments_last_changed() WP 5.0.0

Sets the last changed time for the 'comment' cache group.

No Hooks.

Return

Nothing (null).

Usage

wp_cache_set_comments_last_changed();

Code of wp cache set comments last changed: wp-includes/comment.php WP 5.2.1

<?php
function wp_cache_set_comments_last_changed() {
	wp_cache_set( 'last_changed', microtime(), 'comment' );
}