How to share tickets across & communicate between Technicians?

We operate an IT department where certain technicians are responsible for certain IT functions based over different geographical locations & Timezones.
A lot of our incoming requests come from users expecting a simple change but in fact is a series of changes from different areas of the systems which make up a single ‘user’ request.
Structured requests are simple as we can build a business process to handle it: For example, a new users needs an AD account (Dave) a CRM system account (Paul) etc etc.
Unstructured requests are a little more tricky, for example; a user request is received for printer access request from site A, which requires a change on an RDP server in site B. The Technician on site A is assigned the ticket, but how does he communicate effectively with a technician at site B?

If he re-assigns it, he loses visibility. If he adds notes the technician at site B will not see it. If he (Site A) forwards it to the technician of site B the communication moved outside of the ticket system which is not good.

How does the system deal with this situation, and perhaps a better question – how does the community currently get around this problem?