My Proxy.config file:

<?xml version="1.0" encoding="utf-8" ?>
<ProxyConfig allowedReferers="xxxxxx" mustMatch="true">
    <serverUrls>
     <serverUrl url="https://<server.domain>/arcgis/rest/services/" matchAll="true"/>
    </serverUrls>
</ProxyConfig>


Code from Default.aspx:

    require(["esri/config", "esri/urlUtils"], function (esriConfig, urlUtils) {
        esriConfig.defaults.io.proxyUrl = serverLink + "/Maps/iMapTest/proxy/proxy.ashx";
        esriConfig.defaults.io.alwaysUseProxy = false;
        urlUtils.addProxyRule({
            urlPrefix: dataLink3 + "/Geoprocessing",
            proxyUrl: serverLink + "/Maps/iMapTest/proxy/proxy.ashx"
        });
    });