This paper addresses the challenge of transparent data sharing within computing grids built as cluster federations. On such platforms, the availability of storage resources may change in a dynamic way, often due to hardware failures. We focus on the problem of handling the consistency of replicated data in the presence of failures. We propose a software architecture which decouples consistency management from fault tolerance management. We illustrate this architecture with a case study showing how to design a consistency protocol using fault-tolerant building blocks. As a proof of concept, we describe a prototype implementation of this protocol within JuxMem, a software experimental platform for grid data sharing, and we report on a preliminary experimental evaluation of the proposed approach.