<?php

$string_to_xml = file_get_contents('/home/u/phpDev/simple/home/parser/www/ya.xml', FILE_USE_INCLUDE_PATH);
$xml = simplexml_load_string($string_to_xml);

$i = 0;
foreach($xml->response->results->grouping->group as $a) {
    echo $a->doc->domain . "\n";
    if(preg_match("~sowich\.info~is", $a->doc->domain) == 1) {
        echo '`сайт найден на позиции' . $i;
        break;
    }
    $i++;
}