I'm running XFCE 4.12 with 3 monitors setup into two X screens and two video cards on the same computer. Two of the monitors form a single X screen using nvidia twinview functionality, which is Screen0 on Device0 in the Xorg config. The 3rd monitor is for the second screen which is Screen1 on Device1 in the Xorg config. I can drag windows fine between the monitors on Screen0. I can also move my mouse freely between Screen0 and Screen1 and even the clipboard data is carried between the two X screens ok.
Both of these X screens act as independent desktops which have their own set of viewports. I like it this way and its useful for making one side "stick" automatically. However if I start a program on one X screen, I can't move it to the other X screen by simply dragging it. If I want to run that program on the other screen I have to restart it on that screen.
My question is if there is way to move the program while its running to the other screen using some command or other function of X windows. Thanks.
Update: I'm going to start a bounty on this question but I've been wondering about this for a while. To earn the bounty, you have to provide some citation for proof.