A new post Getting Started with the Coherence Memcached Adaptor from David Felcey shows how PHP memcached calls can automatically be routed to store data in Oracle Coherence 12c. This is possible now Coherence 12.1.3 supports Memcached clients using the Binary Memcached protocol. David's post shows how the Coherence Memcached adaptor can be configured as a proxy service that runs in the Coherence cluster. There's nothing particular to configure in the PHP application, except to enable memcached.use_sasl = 1
So what is Coherence? It is an "in-memory data grid solution", with a number of advanced features. You can read more in the Oracle Coherence 12C Data Sheet.