Some time ago I had problems with providing Web users up-to-date information generated in computed (or computed-for-display) field (named here MY_FIELD) with @DbLookup formula. Well, I didn't want to write any agents refreshing documents or something like that.
The solution of my problem was the use of a hidden computed-for-display field named e.g. "REFRESH_MY_FIELD" located at the top of the form and containing the following formula:
Each time a Web user opens the document the content of MY_FIELD is being refreshed.