An L1 cache (enabled by default, can be disabled) only exists if you set your cache mode to distribution.  An L1 cache prevents unnecessary remote fetching of entries mapped to remote caches by storing them locally for a short time after the first time they are accessed.  By default, entries in L1 have a lifespan of 60,000 milliseconds (though you can configure how long L1 entries are cached for).  L1 entries are also invalidated when the entry is changed elsewhere in the cluster so you are sure you don't have stale entries cached in L1.  Caches with L1 enabled will consult the L1 cache before fetching an entry from a remote cache.

Also known as a near cache in competing distributed cache products.