Magento update custom attribute via API SOAP2

catalog_product_update.php

<?php

$proxy = new SoapClient("http://www.mydomain.com/api/v2_soap/?wsdl");
$sessionId = $proxy->login("myuser", "mypass");

$update_data = array (
    'additional_attributes' => array (
        'single_data' => array (
            array ('key' => 'foreign_visibility', 'value' => '1')
        )
    )
);

// and the update call
$update = $proxy->catalogProductUpdate($sessionId, '2@0215', $update_data);