This notion of content DNS servers having "bailiwicks" is entirely an idiosyncratic invention of Dan Bernstein. BIND doesn't have any such notion.
This is the Frequently Given Answer to that question.
The irony of this foolish "not invented here" attitude is that BIND, in fact, does have the notion of "bailiwick".
BIND tracks the bailiwicks of content DNS servers in order that it can recognise "lame" delegations and bad referrals. If a content DNS server for a domain responds to a query with a referral that is outside of its bailiwick, BIND flags it as a "bad referral" and logs a warning message. That log entry even includes the content server's bailiwick. You should read your BIND logs more closely.
All that Dan Bernstein has done is that he has given this concept a name - a fairly reasonable one, at that.