The original post mentioned "a stream of data" and "if there is garbled data" - hence my suggestion for a checksum.
PeterH:
I still don't understand what difference the UNO's request has made. The Mini is going to keep sending regular messages anyway, isn't it? What problem is the request from the UNO trying to solve?
If it's a "here I am" transmission (I think it has to have enough data in it so the receiver knows it is coming from the correct device) I agree with @PeterH.
You need to carefully consider the failure modes and appropriate responses. If a remote slave device crashes the master can do nothing to restart it. Perhaps you need to use the watchdog timer in the slave. And maybe also in the master. You will also need to consider how you deal with gaps in transmission (or reception) while a WDT restart takes place.
...R