The scrambler is able to process both local URLs, i.e. URLs of documents that reside on the same server, and URLs of documents that reside on other servers. The Web server can easily retrieve a local document and send it to the user. But additional functionality is needed to process external documents.
In the latter case, the Web server has to forward the request to the referenced server, retrieve the requested document, scramble it and send it to the user. For the user, it is not obvious that the requested document doesn't reside on the same server.
This functionality is provided by a proxy server that retrieves requested documents and stores them in a separate cache. This cache accelerates the access to the external resources in case that they are requested again.