Oracle Coherence is a distributed data grid solution, keeping data available in memory, and using sophisticated distribution algorithms and protocols to synchronize and transfer information between its nodes. This model gives us amazing access times by having data readily available and improved reliability by distributing the data between several instances and machines, adding redundancy to avoid loss of information.
The most recent version of WebLogic, 12.1.2, comes with the newest Coherence version, also numbered 12.1.2, and tighter integration between the two products; Coherence is now enabled by default at the server's classpath, working as a regular subsystem like JMS, for instance.