In your root .htaccess:
RewriteEngine on
RewriteRule ^blog/(.*)$ http://www.newdomainyouknow.com/blog/$1 [R=301,L]
OR in your subfolder .htaccess
RewriteEngine on
RewriteRule ^(.*)$ http://www.newdomainyouknow.com/blog/$1 [R=301,L]
You can remove all other entries.
But this will move all request from one domain to the new domain :
for example
http://oldandboringdomain.com/blog/cool-staf
will be redirected to
http://www.newdomainyouknow.com/blog/cool-staf
With 301 redirect (permanent) which mean cachable by the browser and not only.