Scrub pages before returning them to system by default

configname: CONFIG_XEN_SCRUB_PAGES_DEFAULT

Linux Kernel Configuration
└─>Device Drivers
└─>Xen driver support
└─>Scrub pages before returning them to system by default
In linux kernel since version 4.2 (release Date: 2015-08-30)  
Scrub pages before returning them to the system for reuse by
other domains. This makes sure that any confidential data
is not accidentally visible to other domains. It is more
secure, but slightly less efficient. This can be controlled with
xen_scrub_pages=0 parameter and
/sys/devices/system/xen_memory/xen_memory0/scrub_pages.
This option only sets the default value.

If in doubt, say yes.