The manifest file released/1.8.1.xml contains the following bits:
<remote name="apache" fetch="git://github.com/apache/"/>
<remote name="couchbase" fetch="git://10.1.1.210/"/>
<remote name="erlang" fetch="git://github.com/erlang/"/>
<remote name="membase" fetch="git://10.1.1.210/"/>
This cause the file to be usable ONLY for people located in the mountain view office.. If you want to use a local cache you could rather make a local DNS entry to map to that file, put up a proxy server, use an override xml file etc.. there are a lot of workarounds for this.