WordPress at a glance
function is not described

wp_cache_set_posts_last_changed() WP 5.0.0

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

No Hooks.

Return

Nothing (null).

Usage

wp_cache_set_posts_last_changed();

Code of wp cache set posts last changed: wp-includes/post.php VER 5.1.1

<?php
function wp_cache_set_posts_last_changed() {
	wp_cache_set( 'last_changed', microtime(), 'posts' );
}