Does drupal_http_request ever cache results? Does drupal_http_request ever cache results?

I am making a request that looks something like:

$url = "http://www.example.com/some/rest/service?" . drupal_http_build_query(array(
    "id" =&gt; 1234,
));

$options = array(
    "headers" =&gt; array(
        "Pragma" =&gt; "no-cache",
        "Cache-Control" =&gt; "no-cache",
    ),
);

$response = drupal_http_request($url, $options);


The problem is that I am getting back some cached results.  I am not looking for ways to cachebust this request; I am trying to rule out Drupal caching this internally so I can work with the far end to see why their Varnish is being weird.
No, drupal_http_request() is not doing any kind of caching. If the results are cached then it's either the server or some intermediary system, e.g. a proxy.