update_object_term_cache

	foreach ( $taxonomies as $taxonomy ) {
		if ( $clean_taxonomy ) {
			clean_taxonomy_cache( $taxonomy );
		}

		/**
		 * Fires once after each taxonomy's term cache has been cleaned.
		 *
		 * @since 2.5.0
		 * @since 4.5.0 Added the `$clean_taxonomy` parameter.
		 *
		 * @param array  $ids            An array of term IDs.
		 * @param string $taxonomy       Taxonomy slug.
		 * @param bool   $clean_taxonomy Whether or not to clean taxonomy-wide caches
		 */
		do_action( 'clean_term_cache', $ids, $taxonomy, $clean_taxonomy );
	}

	wp_cache_set( 'last_changed', microtime(), 'terms' );
}

/**
 * Clean the caches for a taxonomy.
 *
 * @since 4.9.0
 *
 * @param string $taxonomy Taxonomy slug.
 */
function clean_taxonomy_cache( $taxonomy ) {
	wp_cache_delete( 'all_ids', $taxonomy );
	wp_cache_delete( 'get', $taxonomy );

	// Regenerate cached hierarchy.
	delete_option( "{$taxonomy}_children" );
	_get_term_hierarchy( $taxonomy );

	/**
	 * Fires after a taxonomy's caches have been cleaned.
	 *
	 * @since 4.9.0
	 *
	 * @param string $taxonomy Taxonomy slug.
	 */
	do_action( 'clean_taxonomy_cache', $taxonomy );
}

/**
 * Retrieves the cached term objects for the given object ID.
 *
 * Upstream functions (like get_the_terms() and is_object_in_term()) are
 * responsible for populating the object-term relationship cache. The current
 * function only fetches relationship data that is already in the cache.
 *
 * @since 2.3.0
 * @since 4.7.0 Returns a `WP_Error` object if there's an error with
 *              any of the matched terms.
 *
 * @param int    $id       Term object ID, for example a post, comment, or user ID.