Default is never, equivalent to
<expiry-delay>0</expiry-delay>
Along with the expiration you better set to optimize entries eviction. see local-scheme flush-delay
In your example instead of <local-scheme/>
do something like
<local-scheme>
<expiry-delay>10d</expiry-delay>
<flush-delay>1d</flush-delay>
</local-scheme>
it means that coherence will evict entries 10 days old once a day