Scoping search to just a particular site or list using search service

This is the XML I'm sending right now:

<QueryPacket xmlns="urn:Microsoft.Search.Query" Revision="1">
    <Query domain="QDomain">
        <Context>
            <QueryText language="en-US" type="STRING">testing</QueryText>
        </Context>
        <Range>
            <StartAt>1</StartAt>
            <Count>8</Count>
        </Range>
        <PreQuerySuggestions>true</PreQuerySuggestions>
        <HighlightQuerySuggestions>false</HighlightQuerySuggestions>
    </Query>
</QueryPacket>

The results comes back with everything, but say I only want to scope it to a particular site or list, how would I go about doing it?