Locate an avatar in-world across sim borders?

Forgive me if this has been asked before, but I wasn't able to find what I wanted by searching. Is there a script that I can place in an object in world to create a people locator -- a way to identify where someone is in-world, either in a sim or preferable across sims? Forgive my ignorance, please.

If they're within about 96m (regardless of sim boundary), llSensor can find them (by name, if that's most convenient), and their exact position at time of sensing will be in the corresponding llDetectedPos(). (I suspect that's not quite what's desired, but I don't know a way to do any better.)

Only way I can think of would be for them to wear an attachment/transponder that you could email for position/status information requests. I don't know of any involuntary way of doing this.

llRequestAgentData with the DATA_ONLINE request will tell you whether or not an avatar is online, but not where. You need the avatar's UUID for this.

Mystitool provides a sim scanner which will locate all AVs within a single sim (assuming you have permissions to rez sensors at the requried locations within the sim). It can be used remotely, by rezzing a remote scanner object in the sim you want to scan, which can then be interrogated from elsewhere. But there's no way to use it to scan an arbitrary sim by name, let alone all sims.

My Follow Me script does this. You can pick one up in my store for free. It's Copy-ok so you can copy the script to any object you want. Like all these other solutions, the person you want to follow must be wearing the Follow Me object; there's no way to get a resident's location if they don't want to be found.