Currently, the "S" aspect is interpreted to mean "any usage of sitelinks". So, en:Germany would get purged when Q183 is edited to change the sitelink to frwikibooks, even though en:Germany does not actually have a link to frwikibooks in the sitelinks.
This could be avoided by re-interpreting S to be interpreted as "sitelinks used in the sidebar", which currently means "wikis in the same group" plus "wikis in the same language in other group" (plus possibly a handful more, like commonswiki).