iptables DNAT reply translation query

I'm confused while trying to understand the DNAT mechanism under below circumstance.

My understanding:

DNAT -> Destination Network Address Translation - Functionality which translates the dst address of the incoming packets --to--destination x.

I am facing difficulty in understanding the DNAT reply path.

For E.G

I have a machine (A) with an IP of x1 and wanted all connections/packets coming to this machine (dest y1) to get rerouted to another machine (B) with an IP address of z1.

So I added a new NAT rule as below:

iptables -t nat -A PREROUTING -s x1 -d y1 -j DNAT --to-destination z1.

Test on MACHINE A >ping -I x1 y1

if I run "tcpdump -i eth6 icmp" on machine A then getting an reply from IP "y1" instead z1?? or it is something that the un-NAT is performed based on the subnet mask ?

And when I monitored "tcpdump -i eth6 host z1" there isn't any incoming ping or packet.

Could someone clarify this scenario and my understanding ?

And also, is there anyway we can make this tcpdump if the packet is locally translated ?

Thanks in Advance.