7.4.1 & invalid page header in block

Hi,

I use the 7.4.1 version of postgresql.
And I got few message in log:
# grep header log
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4602 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4598 of relation "url"
ERROR:  invalid page header in block 4602 of relation "url"

url is a index for web. I do not care if I loose few data.

How can I correct table url ?

Thanks for any help.

Jean-Gérard Pailloncy