CONFIG_OUTER_CACHE_SYNC is not available for thedefaultarchitecture x86.
Result is shown for architecture arm

CONFIG_OUTER_CACHE_SYNC (not configurable)

configname: CONFIG_OUTER_CACHE_SYNC

Linux Kernel Configuration
└─>OUTER_CACHE_SYNC
In linux kernel since version 2.6.34 (release Date: 2010-05-16)  
The outer cache has a outer_cache_fns.sync function pointer
that can be used to drain the write buffer of the outer cache.

is depended by
CONFIG_CACHE_L2X0