Data replication is an important aspect in a Data Grid for increasing fault tolerance and availability. Many Grid replication tools or middleware systems deal with read-only files which implies that replicated data items are always consistent. However, there are several applications that do require updates to existing data and the respective replicas. In this article we present a replica consistency service that allows for replica updates in a single-master scenario with lazy update synchronisation. The system allows for updates of (heterogeneous) relational databases, and it is designed to support flat files as well. It keeps remote replicas synchronised and partially ("lazily") consistent. We report on the design and implementation of a novel "relaxed" replica consistency service and show its usefulness in a typical application use case.