While it is not documented, sample code is shipped in sysviewHLQ.CNM4BREX(TESTAPI) that uses a clear screen function. In SYSVIEW's load library (sysviewHLQ.CNM4BLOD) a program is shipped called GSVXCSCN. If the REXX which is running has access to SYSVIEW's load library, then the program can be called and the screen will be cleared. This is done through the SYSVIEW REXX API or can be invoked in any TSO REXX type environment. The following must be added when a clear screen is desired:
ADDRESS TSO GSVXCSCN
Please note, the screen clear will be somewhat asynchronous to inline REXX. If data is being outputted very quickly, the screen clear might not line up with where it is coded all the time. Unfortunately, TSO is in control of the output and the clear.