Precise and Imprecise Interrupt

I have a question regarding precise and imprecise interrupts. This is what i read:

Note that there is no prohibition on instructions beyond the one pointed to by the PC from starting. It is just that any changes they make to registers or memory must be undone before the interrupt happens. It is permitted that the instruction pointed to has been executed. It is also permitted that it has not been executed. (Taken from Mode Operating Systems book by Andrew S. Tenenbaum pg.349)

My question is: How do you perform this 'undone' process?

• Does it simply clears off the undone instructions that reside above the Program Counter?
• Or does it conceal the incomplete instructions to give it a façade that all the instructions that lie after PC have been fully executed and the ones that come before it have not been executed?
• Or it uses another technique to give it an illusion of sequential instruction execution?

Small question: If the second one is the correct answer, isn't it quite similar to imprecise interrupt?

I have read books, blogs, and websites regarding this, albeit i still couldn't find an answer to my doubt. Can anyone shed some light on this matter?

Thanks in advance.