gistfile1.php

<?php
/**
 * Switch the interal blog id.
 *
 * This changes the blog id used to create keys in blog specific groups.
 *
 * @since 3.5.0
 *
 * @param int $blog_id Blog ID
 */
function wp_cache_switch_to_blog( $blog_id ) {
	global $wp_object_cache;

	return $wp_object_cache->switch_to_blog( $blog_id );
}

class WP_Object_Cache {
	/* ... */
	function switch_to_blog( $blog_id ) {
		global $table_prefix;
		$blog_id = (int) $blog_id;
		$this->blog_prefix = WP_MEMCACHED_KEY_SALT.':';
		$this->blog_prefix .= ( is_multisite() ? $blog_id : $table_prefix ) . ':';
	}
	/* ... */
	
}