private void invalidateCache(Request req) {
        dispatchRpcRequest(req, () -> {
            proxyServer.memoryCache().clear();
            String[] s = new String[2];
            s[0] = "0";
            s[1] = "success";
            req.returnValues().add(new StringArray(s));
            req.returnRequest();
        });
    }
Returns 0 if server is alive.

@param req a Request
config-proxy/src/main/java/com/yahoo/vespa/config/proxy/ConfigProxyRpcServer.java