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There is a global variable called $pagenow for the use within WP Admin:

global $pagenow;
if ( $pagenow == 'upload.php' ) :

    function custom_admin_notice() {
        echo '<div class="updated"><p>Updated!</p></div>';
    }
    add_action( 'admin_notices', 'custom_admin_notice' );

endif;

UPDATE: Simply include the snippet in your themes or plugins functions.php