Arthur van Hoff, CTO of Marimba Inc., was the one who helpfully directed me to the prior art which convinced me that the Hash Cache concept had already been invented. The HTTP Distribution and Replication Protocol document, submitted to the W3C two months prior to my date of conception, describes the mechanism as part of a larger recommendation.
Unfortunately, some three years later, we have yet to see this idea implemented as a common feature of web browsers. It is my hope that the publication of this abandoned patent application will further use of a process which could, through the efficient use of bandwidth consumption, promote the proliferation of more advanced online applications.
The source code for my Hash Cache research efforts is available from the ORBS Open Source Java repository.