Add global menu using network-wide-menu

gistfile1.php

<?php
/* 
register the menu across the network
*/
register_nav_menu( 'global', 'Global Navigation Menu' );

/* 
remove the menu from the menu screen on sub sites to avoid confusing users
*/
add_action( 'admin_init', 'global_nav_menu_init' );

function global_nav_menu_init(){

  if ( ! is_main_site() )
		unregister_nav_menu( 'global' );

}

gistfile2.php

<div class="global-nav-menu">
  <?php
  wp_nav_menu( 'global' );
  ?>
</div><!-- global-nav-menu -->