In that case
I access the popup page from parent page 1 and click 90 row in IR popup and . but when I try to access the same IR popup from page 2. the IR still show the 90th row rather than one.
fac586 is correct.
APEX URL Syntax: f?p=App:Page:Session:Request:Debug:ClearCache:itemNames:itemValues:PrinterFriendly
I hope you are passing a URL link from java script in page1 and page2. You can pass RP in ClearCache section in that URL.
for example, f?p=&APP_ID.:3:&APP_SESSION.:::RP:::
If your IR is not based on any item values then you can create a Reset Pagination process. Refer the link 8.5 Understanding Page Processes.
If possible share your java script where you are calling the IR page.
Thanks a lot.