delete-transient.php

<?php

if ( is_multisite() ) {
    global $wpdb;

    $all_sites = $wpdb->get_results( "SELECT * FROM $wpdb->blogs" );

    if ( $all_sites ) {
        foreach ($all_sites as $site) {
            $wpdb->set_blog_id( $site->blog_id );
            $wpdb->query( "DELETE FROM `{$wpdb->prefix}options` WHERE `option_name` LIKE ('_transient_%')" );
        }
    }
}