Question

The transactions that span across multiple services are handled by in microservice

Answer 1

Micro service do business unit of work where transaction limits in maximum ways will span a business unit of work so the transactions are automatically within a service.  

A "debit savings bank account" operation can be atomic and transaction can be verified as that operation is within boundary of service.

There are business that require you to run business units of work across multiple services and such orchestration spans across areas of different services thus verifying transaction security is a challenge.