// If this node thinks the primary is someone we haven't tried, make that the next
    // hostToScan.
    if (!reply.primary.empty() && !_scan->triedHosts.count(reply.primary)) {
        std::deque<HostAndPort>::iterator it = std::stable_partition(
            _scan->hostsToScan.begin(), _scan->hostsToScan.end(), HostIs(reply.primary));

        if (it == _scan->hostsToScan.begin()) {
            // reply.primary wasn't in hostsToScan
            _scan->hostsToScan.push_front(reply.primary);
        }
    }