DNS question...
 

Hi all,
Say if i have a domain and i changed the registrar from nameserver1 to nameserver2.

For example, if a client side cache isn't cleared, and if the client requests DNS query, would it be possible for the old nameserver1 to respond to the query? would nameserver1 never respond to DNS request?

Well there's no "never " but DNS is certainly subject to ttl settings being honoured by intermediate DNS servers and the likes so you can never guarantee an immediate, or even timely, update to affect every end user.