Most likely, these "old screens" are just messages you did not receive when you were expecting them. This might be because you logged off, the system is processing your input or the output, or your input message was put in queue and you did not receive it immediately. Later, when the program processes your message and sends a reply, it will be sent to your terminal.
Is there any command I can use to clear such kind of data or Queue?
You could clear the messages in queue, which is most probably not what you are looking for. My suggestion is to just live with it... it is a quality part of IMS . During work, just try not to submit your messages twice, especially when you don't get a response immediately.
What do you mean by this? You can usually clear the screen by pressing the 'break' key on the keyboard.
To delete the messages in your queue, stop your user and use the '/DEQ USER PURGE' or '/DEQ USER LTERM lterm PURGE' command. As a regular user you usually don't have the right to issue these commands. And, as mentioned before, it is not intended to be used as a regular process