Page 10 of the PCI DSS v3.1 states:
"The PCI DSS security requirements apply to all system components included in or connected to the cardholder data environment. The cardholder data environment (CDE) is comprised of people, processes and technologies that store, process, or transmit cardholder data or sensitive authentication data."
So your systems are indeed in scope for PCI because they transmit cardholder data.
Since all the cardholder data is stored by your cloud provider you don't have to worry about any storage requirements for the cardholder data (encryption and key management).
You DO however have to worry about your logging. Since your machines are used to connect to the CDE they're brought in scope. Logs of all in scope systems COULD be stored locally on each end point, but enforcing the rest of the requirements for logs becomes very hard if they're not centrally managed.
Secure audit trails so they cannot be altered.
Retain audit trail history for at least one year, with a minimum of three months immediately available for analysis (for example, online, archived, or restorable from backup).
You don't have to store log backups off site and depending on your companies risk assessment it might not be cost effective to do so, but I would highly recommend storing them on a centrally managed system that is access controlled.
Edit - added clarification about 9.5.1 so people don't have to sift through comments (Thanks @SilverlightFox)
The heading for requirement 9 states
“Media” refers to all paper and electronic media containing cardholder data.
Since there isn't any cardholder data being backed up or even stored in the first place requirement 9.5.1 would be N/A because the "media" doesn't contain cardholder data.